Process of leaching copper ores.



A. w. HAHN.\ PROCESS 0F LEACHING COPPER GRES.

APPLICATION FILED` JAN. 9. I9! 5- a citizen ot' the united States, residing at UNITED STATES PATEN ermee f1 'To all 'whom 'it ma concern v vBe it known tiat I, ALBERT W. HAHN,

El Paso, in the county of El Paso and State of Texas, have invented` certain new and useful Improvements in Processes of Leaching Copper Ores, of which the following is a i specification.

This invention relates to a method of recovering copper by the electrolysis of vco per solutions of any suitable kind, obtaine Vthe lixiviation of the ore; and it 4consists in the operations and sequences of operations yset forth in the specification and claims.

I contemplate a treatment of the ore, particularly `a low grade ore, in the usual manner. Accordingly, if the ore is an oxid, or one which contains no compound of copper with sulfur, it can be treated direct with hthe leaching solution. If the copper is resent as a ysulfid the ore must be roasted 1n order to make the copper soluble in the lixiviant. The'ore is crushed and if necessary roasted so that the copper is in the form of oxids and sulfates. The present method involves the leaching of the ore in such a way as to keep down the l,ferrie iron,

ialuminum and arsenic content of the soluwhich passes tl'irough the tanks in succes tion so as to avoid the reduction of ampere eliic1ency 1n the electrolytic tank due to the continuous oxldation of the iron at the anode andthe reduction of the iron at the cathode, by the copper itself, and so as to avoid the deleterious effects resulting from accumulation of aluminum and arsenic in solution.

One of the objects of the invention is to provide a continuous process according to which ore in a series of tanks orthe like is subjected to the action of leaching solution,

sion, whereby all' or practically all of the free sulf'uric acid or other leaching agent `of my process.

- Specication of Letten Patent.

'i prevention of raocnss or Lemma corran onEs.

Patenten of. 1; .`22, 1918. f f; y ppucauun :um Jgnunrys, 11915.- ,serm nu. 1,219.

iron.

For themsake of clearness I shall describe the process with reference to the accoman'accumulation of ferrous y panying drawing, in which there is shown diagrammatically a lay out of a plant or A installation in whichthe method maybe carried out.

In ythe diagram thereis showna series of eight leaching tanks, though it-should be understood that the series-leaching 'hereinafter explained mav be accomplished in any` other form of leaching apparatus, as

troughs, classifiers or thickeners, and in any Yusual or preferred way. The number of.

tanks in the series will be determined by the grade of the ore,'or the number of days required for-leaching out the copper, and the size of the tanks will be in accordance with thedaily capacity of the plant. The leaching tanks have been numbered in the diagram Nos. 1, 2, 3, 4,' 5, (5, 7 and 8, and there are also shown included in the system two storage tanks for wash-water, one regen-y erated solution tank, one electrolytic circula-y tion tank, and an electrolytic tank. Each leaching tank has a circulation pump, which circulates the solution through the ore; the overflowing solution goes back to the circulation pump, except a certain quantity which is'advanced to the next tank in the series.

In beginning operations, thev tanks are filled Wlth ore in proper condition. A' 2.5

percent. solution of Vsulfuric acid is now' y added totank No. 1, and circulated through the ore for twenty-four hours. 0n the sec ond day the solution from tank No. l is advanced to No. 2, and enough fresh solution advanced for No. 1'1" -At the end of forty-eight hours the solution from No. 2 tank is advanced to No; 3 tank, and vif it is neutral it is brought to 2.5 per cent. strength by the addition of fresh acid. During all `this time acid` solution has been coming through No. l'tank to No. 2, and now from No. Qito No. 3. At the end of seventy-two` i hours, No. el tank is cut. in, and solution. from tank No. 3 advanced toit. Solution is now passing through four tanks. At the end of ninety-six hours No. 5 tank is cut in, and solution advanced to it from No. 4 tank,

`and we now have five tanks, all circulatingl solution. Assuming that it requires six days to properly leach the ore, six tanks will be put 1n series, 1as above, and solution will acid than No. 3; No. 5 one day, with less` acid than No. 4; No. 6 has beenstanding` empty and is now `filled with fresh ore and receiving the solution loW in acid or neutral., from No. 8, and is almost neutral; No. 7 is being emptied of ore that has been leached six days andwashed the previous day; and No. 8 contains ore which has just finished its sixth day of the leach and is being Washed. There is in the electrolytic tank, solution which runs`1.5 per cent. copper, three per cent. free sulfuric acid, 0.25 per cent. ferrous iron, and 0.25 per cent. ferric iron. The solution in the electrolytic tank is circulated continuously, and a portion is continuously sent to the regenerated' solution tank, whence it in turn passes to tank No. 6. All six tanks containing ore have solution goingthrough them. The rate of flow is governed by the amount of co per in the ore, and the same fiow is maintained' throughout the system, so that the amount of solution going to the regenerated solution tank from the electrolytic tanks is equal to that coming olf from tank No. 6 and going to the electrolytic tank, tanks No. 7 and 8 being for the present out of the solution circuit.

With the circuit thus established, I withdraw from the circuit each day the tank which has been longest under leach, and out in a tank of fresh ore, so that there will '1l- Ways be (in the present example), six tanks in circuit, one filling, and one emptying, and being washed. Thus, on the seventh dayNo. 1 tank will be cut 'out of the circuit, for lWashing and emptying, No. 2 will have in itore that has been under leach five days, No. 3, four days, No. 4 three days, No. 5 two days, No. 6 oneday, No. 7 will have a charge of fresh ore just beginning the leach,

and No. 8 will be filling Withfresh ore, and i with No. 1 Will be out of the solution circuit. And so on from day to day. The result is that the solution, before reaching the electrolytic tank, passes through six tanks,

and in the last of the six it encounters a batch of fresh ore. The solution, in going from the first tank to the sixth, necessarily changes, that is, the acid content decreases, the copper increases, the ferrous iron increases, and the ferric iron increases up to the fourth tank, and then sharply decreases.

vThis last result is due to the fact that the ferric iron begins to precipitate,if there is less than 0.50 per cent. of free acid in the solution when it comes in contact with the oxidized copper, &c., in the sixth tank. The whole Object of the series of tanks, and the cutting out ofthe exhausted tank and cut- -ting in of a fresh tank daily, is to have the NeutmZz'z-lz'ng and precipitating tanja.

scuo+re, so.),=

v e 30u804 Fe,O,(melaconite),

Aluminum is precipitated probably as a hydrate, basic or perbasic salt, which is insoluble in a 2.5 er cent. solution of sulfuric acid, and arsenic probably as a ferric arse-Y nite, also insoluble in a 2.5 per cent. solution of sulfuric acid. The ferric iron is thus precipitated, and the solution coming off from the sixth or neutralizingand precipitating tank, low in ferric iron,l goes to the electrolytic tanks, Where the oxygen given off at the anode will `oxidize the ferrous iron to ferric iron, and the ferric iron Will in turn attack the copper of the cathode:

Electrolytzc tank.. l

2FeSO4 O HZSO4 Fe2(SO4)3 H2O Cu Fez (S04), i- CuSO4 2FeSO4.

kThus ferrous iron is formed, so that the solution coming from the electrolytic tanks will have its'i'ron approximating one half in the ferrous and one half in the ferric state.v When it again makes the circuit of the ore practically all of the ferric iron in the regenerated solution will be precipitated, together with any taken up from the ore. In lthis Way the iron may be kept lo1 in the electrolyte.

Theelectrolytic circuit will be a closed solution circuit, made acid by the addition of sulfuricV acid before the solution Varrives at the electrolytic tank, because too much power is consumed in electrolyzing' a neutral solution or one low in acid. Thus the electrolyte as it is sent to the regenerated solution-storage,contains about three per cent. free sulfuric acid. There is, however, daily a quantity of Wash-Water from the leached ore in the tank last cut out of the solution circuit, and the regenerated solution is mixed with the wash-water, bringing the acid down to the desired 2.5 per cent.

It will be evident that the process is in part Ato based on neutralizing the leaching solution by the ore itself, before it goes to the electrolytic tank, and upon the discovery that the ferrie iron content precipitates from the neutral or nearly neutral solution when brought into contact with an oxid of copper,

and that this iron, so precipitated, is in-` goes on ore which has alread been leached 4 for a number of da s, and t e almost neutral solution is app ied to fresh ore. The oxidation of a` portion of the ferrous iron in the electrolytic circuit is alsoimportant in thc successful Working of the process.

I claim:

1.. The method which consists in providing a number of tanl' in series circult, each containing ore, progressively advanclng acidleaching solution through the series, neutralizing the solution in the last tank of the series by contact With the ore therein itself to render the ferrie iron content of the solution permanently insoluble in the acidleaching solution and precipitating the ferric iron contents, leadingthe solution, minus such precipitated ferrie iron, to an electrolytic cell, and then electrolyzing the solution, and -sending it back to cert-ain of the tanks.

2. The method which consists in providing a number of tanks in series circuit, each containing ore, progressivel advancingacidleaching solution through t e'seri'es, neutralizing the solution in the last tank of the series by contact with the ore therein itself to render the ferrie iron content ofthe solution permanently insoluble in the acid-leaching solution, and precipitating the ferri'c iron contents, adding acid, leading the strengthened solution, minus such recipitated ferrie iron, to an electrolytic cellpand then electrolyzing t-he solution inthe cell, regenerating and sending it back over the circuit.

3. The method which consists in providing a number of tanks in series circuit, each containing o re, progressively advancing acid-leaching solution through the series neutralizing the solution in the last tank of the series b contact with the or'e therein itself to reni er the ferrie iron content of the solution permanently insoluble in the acidleaching solution and precipitating the ferric iron contents, leading the solution, minus such precipitated ferrie iron, to an electrolytic cell, and then electrolyzing the solution and sending it back over the c1rcuit, and at intervals cutting the first tank of the series out of the circuit and cutting into the circuit a tank of fresh ore, such fresh tank becoming, in each instance, the last of the series and thesolution discharging therefrom being electrolyzed .I

4. The method which consists in advancing acid-leaching solution progressively through a series of `ore containers, containing respectively ore in progressively differ-` en t conditions of exhaustion, the first container containing ore which is practically exhausted or leached out and the last containing fresh ore, whereby the strength of7l5 the leaching solution decreases from the first to the last tank progressively and in the last 'tank is neutral, causing the precipitation of the ferrie iron contents of the solution by contact with the ore in said tank itself, adding acid, electrolyzin the solution thus purified and strengthened and sending it back'to 'the first tank.

5. The method which consists in advancing acid-leaching solution progressively through a series of ore containers containing respectively ore in progressively different conditions of exhaustion, the first container` containing ore which is practically exhausted or leached out and the last containing fresh ore, whereby the strength of the leaching solution decreases from the first to thelast tank progressively and in the last tank is neutral, causing the precipitation of the ferric iron contents of the solution by contact With the ore in said tank itself, adding acid, electrolyzing the solution thus purified and" strengthened and sending it back .to the first tank and at intervals cutting the first tank of the series out of the circuit and cuttin into the circuit a. tank of fresh ore, such resh tank becoming in each instance the last of the series and-the purified solucipitation of the ferric iron contents of the" solution and sending the solution thus freed. fromsch ferrie iron content to the electrolytic cell.

7. The method of treating an acid-leaching solution in circulation through a series of tanks of ore, which consists in rendering the solution neutral in the last tank of theseries and treating it. with copper-bearing material to render the ferric iron permanently insoluble in the leaching solution, electrolyping and regenerating, and sending it back to the first tank.

8., The method of treating an acid-leaching solution in circulation through a series Qfltmanks of,ore,;,which consists in renderinglO n the solution neutral in the last tank of the series, treating it with copper-bearing mute rial to render the ferrie iron permanently insoluble in the leaching solution,. adding acid to thev Solution, electrolyzingl "and regenerating,4 and sending it back to the first tank und at intervals .cutting out the first tank from the series, and cutting in :L tank of fresh ore into the'circuit, which becomes the last of the Series,

9. The cyclic method which comprises circulating acid-leaching solution through ore until it becomes neutral, then causing it to pass through a fresh charge of ore Whereb ferrie iron is rendered insoluble and precipi l5 tatecl, adding acid to the -Solution thus freed from ferric iron, eleetrolyzing, and :sendingr the solution back to the ore again.

' In testimony whereof I affix my signa-ture in presence of ltwo Witnesses.

' ALBERT W. HAHN.

Witnesses:

C. A. SANTZ, H. C. ENOS. 

